The present invention relates in general to substrate manufacturing technologies and in particular to methods and apparatus for improving process results by compensating for edge ring wear in a plasma processing chamber.
In the processing of a substrate, e.g., a semiconductor wafer or a glass panel such as one used in flat panel display manufacturing, plasma is often employed.
As part of the processing of a semiconductor wafer, for example, the wafer is divided into a plurality of dies, or rectangular areas, each of which will become an integrated circuit. The wafer is processed in a series of steps in which materials are selectively removed (etching) and deposited (deposition) in order to form electrical components thereon.
In an exemplary plasma etching process, the wafer is coated with a thin film of hardened emulsion (i.e., such as a photoresist mask) prior to etching. Areas of the hardened emulsion are then selectively removed, causing parts of the underlying layer to become exposed. The wafer is then placed in a plasma processing chamber on a negatively charged electrode, called a chuck. Appropriate etchant source gases are then flowed into the chamber and struck to form a plasma to etch exposed areas of the underlying layer(s). In an exemplary plasma deposition process, plasma is also employed to facilitate and/or improve deposition from the source deposition materials.
In many plasma processing chambers, an edge ring is often employed. To facilitate discussion, FIG. 1 illustrates a simplified cross section view of a plasma processing chamber 100. A wafer 104 sits on a chuck 112 which supports the wafer in the plasma processing chamber. Chuck 112 acts as a work piece holder and may be electrically energized by an RF power source to facilitate etching and deposition, as is well known. A coupling ring 108 is shown disposed between chuck 112 and a ceramic ring 110. One of the functions of coupling ring 108 includes providing a current path from chuck 112 to an edge ring 102. Edge ring 102 performs many functions, including positioning wafer 104 on chuck 112 and shielding the underlying components not protected by the wafer itself from being damaged by the ions of the plasma.
One important function of edge ring 112 relates to its effect on process uniformity across the substrate. It is well known that the equipotential lines of the plasma sheath 106 curve upward sharply past the edge of the chuck. Without an edge ring, the substrate edge electrically defines the outer edge of the chuck, and the equipotential lines would curve upward sharply in the vicinity of the substrate edge. As such, areas of the substrate around the substrate edge would experience a different plasma environment from the plasma environment that exists at the center of substrate, thereby contributing to poor process uniformity across the substrate surface.
By electrically extending the plasma-facing area of the chuck with an edge ring and/or other underlying structures, the edge of the chuck appears electrically to the plasma to extend some distance outside of the edge of the substrate. Thus, the equipotential lines of the plasma sheath stays more constant over the entire surface of the substrate, thereby contributing to process uniformity across the substrate surface.
Unfortunately, edge rings tend to be worn away over time by the plasma environment. As the edge ring wears away, the plasma environment in the vicinity of the damaged regions of the edge ring changes. The change to the plasma in turn causes the process result to change over time, and contributes to process degradation as the edge ring wears away. This is the case even if the process employs the same recipe in the same chamber time after time.
Over time, the process result degrades to the point where an edge ring change is necessary. When an edge ring change is required, substrate processing is brought to a halt, and the plasma processing chamber is taken out of service in order to facilitate an edge ring change. During the edge ring change operation, which may take hours or days, the manufacturer is deprived of the use of the affected plasma processing system, which contributes to a higher cost of ownership for the plasma processing system.
In view of the foregoing, there are desired improved methods and apparatus for improving process results in a plasma processing system that employs edge rings, as well as for reducing the frequency with which an edge ring change is required.